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THIS IS OUTDATED INFORMATION GO HERE > https://github.com/xaya/xaya/tree/master/doc/xaya

Blockchain Consensus Protocol

This document gives an overview of the low-level consensus protocol implemented by the core Xaya daemon.

NOTE: The final reference for the protocol is the Xaya Core implementation. This document just highlights the most important parts in an easy-to-read form.

Xaya Is Based on Namecoin

Most parts of the Xaya consensus protocol are inherited from Namecoin, which itself inherits most of the Bitcoin protocol.

As with Bitcoin, Namecoin and Xaya implement a distributed ledger by tracking the current set of "unspent transaction outputs". However, in addition to pure currency transactions, they also implement a name-value database. This database is stored and updated similar to the UTXO set. Each entry contains the following fields:

  • Name: A byte array with restrictions that is the "key" for the name-value-database. In Xaya, this is typically the account name of a player. It can be up to 256 bytes.
  • Value: Another, typically longer, byte array (also with restrictions) that holds data associated with the name. In Xaya, this is used to store a player's latest moves or other actions. It can be up to 2,048 bytes.
  • Address: Similar to transaction outputs, each name is associated with a Xaya address (Bitcoin script) that "owns" it. Only the owner has write access to this name's entry, while everyone can read it from the database. The owner can send the name to a different address, either one of their own or to someone else's.

In addition to spending and creating currency outputs, each transaction can optionally also register or update a name in the database. A single transaction can at most affect one name. A name can be updated at most once per block.

Specific details for the transaction format are not provided here because they are the same as in Namecoin.

In contrast to Namecoin, which registers names in a two-step process (name_new and name_firstupdate), Xaya's name registrations are always done in a single transaction (called name_register). This transaction is similar to a name_update in Namecoin except that it does not consume a name input.

Basic Differences from Bitcoin

Some of the basic chain parameters and properties of the genesis block in Xaya differ from those in Bitcoin and Namecoin. Furthermore, some of these details were changed in the past with scheduled forks. The current parameters for mainnet are:

  • PoW mining is done based on triple-purpose mining.
  • The difficulty is updated for each block using the Dark Gravity Wave (DGW) formula.
  • Blocks are scheduled to be produced, on average, every 30 seconds instead of every 10 minutes. Difficulty retargets independently for each of the two possible mining algorithms. Merge mined SHA-256d blocks are scheduled once every two minutes and standalone Neoscrypt blocks every 40 seconds.
  • The initial block reward is set to 3.82934346 CHI, and halves every 4.2 million blocks, which corresponds to Bitcoin's halving of once every four years. This reward was chosen to yield the correct total coin supply following the token sale.
  • The genesis block's coinbase transaction pays to a multisig address owned by the Xaya team. Unlike Bitcoin and Namecoin, it is actually spendable, and does not observe the usual "block maturity" rule.
    • These coins will be distributed to the community according to the token sale and Huntercoin snapshot. Unsold coins will be destroyed by sending them to a provably unspendable script (OP_RETURN).
  • The maximum block weight is 400,000 instead of 4 million, corresponding to a block size of 100 KB instead of 1 MB. The maximum number of sigops in a block is 8,000.
  • The maximum size of a script element is 2,048 bytes instead of 520 bytes, primarily to allow for larger name values.

Activation of Soft Forks

Xaya immediately activates some of the soft forks introduced in Bitcoin over time since we start with a fresh blockchain:

(Note that some of these activate later or never on the regtest network to allow for certain tests to be possible.)

Name and Value Restrictions

Valid names and values in Xaya must satisfy additional constraints compared to Namecoin, which only enforces maximum lengths. In particular, these conditions must be met by names and values:

  • Names can be up to 256 bytes long and values up to 2,048 bytes.
  • Names must have a namespace. This means that they must start with one or more lower-case letters and /. Expressed as a regexp, this means they must match: [a-z]+\/.*
  • Names must be valid UTF-8 and must not contain unprintable ASCII characters, i.e. those with a value less than 0x20.
  • Values must be valid JSON and parse to a JSON object.